IJE TRANSACTIONS A: Basics Vol. 31, No. 4, (April 2018) 679-683

Please cite this article as: Y. Adriansyah, Z. Zakaria, D. Muslim, F. Hirnawan, Determining of Geotechnical Domain Based on Joint Density and Fault Orientation at Batu Hijau Mine,West Sumbawa-Indonesia,International Journal of Engineering (IJE),IJE TRANSACTIONS A: Basics Vol. 31, No. 4, (April 2018) 679-683

International Journal of Engineering

J o u r n a l H o m e p a g e : w w w . i j e . i r

Determining of Geotechnical Domain Based on Joint Density and Fault Orientation

at Batu Hijau Mine,West Sumbawa-Indonesia

Y. Adriansyah*, Z. Zakaria, D. Muslim, F. Hirnawan

Faculty of Geological Engineering, Padjadjaran University Bandung, Indonesia

P A P E R I N F O

Paper history: Received 14 October 2017 Received in revised form 02 January 2018 Accepted 04 January 2018

Keywords: Batu Hijau Mine Geotechnical Domain Geotechnical Mapping

A B S T R A C T

The research area is located at Batu Hijau Mine – PT Amman Mineral Nusa Tenggara, administratively

located at the southwestern of Sumbawa, West Nusa Tenggara Province – Indonesia. The research area

is controlled by tectonism in accordance to close with the active tectonic plate at southern part of this island. The presence of the active tectonic regime causes of the rich deposit of ore mineralization and

intensive of geological structure in this region. The study was focused on how to develop geotechnical

domain which is an important aspect for developing of open pit mine design. The data collecting methods are obtaining by the window and scanline geotechnical mapping in line with excavation stage

to execute pit slope design. The research result shows that the geological information is very useful to

determine the geotechnical domain. It can be used for guidance on developing pit slope design parameter in open pit mining, and other geotechnical purpose such as defining probability of failure,

slope movement guidance, and risk assessment.

doi: 10.5829/ije.2018.31.04a.21

1. INTRODUCTION1

The Batu Hijau Mine is one of the biggest copper-gold

mine in Indonesia which operated by PT Amman

Mineral Nusa Tenggara (PTAMNT). The mine site is

located at the southwestern part of the Sumbawa Island,

West Nusa Tenggara Province – Indonesia. Based on

the geological and geotechnical perspective, the Batu

Hijau Mine area is very unique because all of the

geological aspect are significantly impacted to the ore

deposit condition and pit wall instability event.

The above conditions may be strongly influenced by

the subduction zone from the active tectonic plates

which located in the southwestern of the study area.

Garwin [1] describes the Sumbawa Island lies at the

major structural discontinuity in the Sunda-Banda arc,

which is characterized by a reversal in polarity of recent

volcanism by the intersection of northeasterly and

northwesterly oriented arc-transverse tectonic

lineaments (Figure 1).

*Corresponding Author’s Email:yan.adriansyah74@gmail.com(Y.

Adriansyah)

Scan-line mapping is one of the common methods to

obtain geotechnical information to assess pit wall

performance and stability. However, the geotechnical

information is not only useful for the purpose of slope

stability, but, it can be used for another purpose. This

study was focused on verifying the impact of the

geological structure into the ore-grade distribution at

Batu Hijau Mine area as one of the Au-Cu porphyry ore

deposit type in Indonesia.

Figure 1. Map showing the tectonic element at the Batu Hijau

district on the Sumbawa Island (Modified from Garwin)

TECHNICAL

NOTE

Y. Adriansyah et al./ IJE TRANSACTIONS A: Basics Vol. 31, No. 4, (April 2018) 679-683 680

Geological information is one of the fundamental

controls on supporting developing of pit slope design.

According to Dearman [2], the characteristic data that

need to be collected for engineering geological

requirement has to be assembled for the following

aspect: lithology, structure, and fault. In addition, there

are important aspects of geological information that

need to be understood such as description of lithological

units, presence of characteristics of fracture, presence of

micro structure (fault), and orientation of variation of in

situ stresses [3].

2. METHOD

2. 1. Mapping of Joint Density The density of joint

was obtained from the geotechnical mapping data which

is taken from the outcrop along the bench, hauling

ramp, slope-break where geological features exposed on

the face above the broken rock [4], and other area that

still possible to be mapped by considering to the safety

requirement.

2. 2. Structural Model Structural model was

generated from the surface and sub surface data. The

geotechnical scan line mapping was conducted to obtain

the surface data, meanwhile the sub surface data of

geological structure was obtained from the oriented

geotechnical drilling. Both types of data will be used for

constructing the structural model which was conducted

into 2 steps that are; surface and sub-surface

interpretation (Figure 2). The surface interpretation was generated from the

scan line geotechnical mapping on the exposed pit wall

that recorded field information about any structure

appearances. The data was interpreted and modeled on

the 2D mode based on the azimuth and other fault

parameter. Furthermore, the subsurface interpretation

was conducted based on the structural geology data

from the oriented geotechnical drilling. As a result, a 3D

wire framing of structural model was constructed and

generated. The process was conducted by using

MineSight®.

In term of the size of structural geology in Batu

Hijau Mine, the faults are categorized into 2 types

namely; major fault and intermediate fault. For

geotechnical purpose, all these faults are continuously

reviewed and updated based on the new available data

that exposed on the wall.

2. 3. LITHOLOGY Generally, the lithology at Batu

Hijau Mine can be classified into Volcanic, Diorite and

Tonalite (Figure 3). Volcanic rock is the oldest and

dominates rock composition at the research area. At the

north-eastern part, these rocks are intruded by quartz

diorite and continued with a series of Porphyry intrusion

Tonalite breaking through the contact zone between

Andesite and diorite.

Figure 2. Surface interpretation using scan-line geotechnical

mapping and subsurface interpretation from oriented

geotechnical drilling data

Figure 3. Lithology map showing rock type distribution at

Batu Hijau Mine (Modify from Q1 Mine Geology

Compilation Map, 2017)

Most of the mineralization process associated with the

initial intrusion Tonalite rocks (Old-intermediate

Tonalite) which is characterized by the presence of

quartz veins intensively, whereas Tonalite end intrusion

(Young Tonalite) tend to be associated with

mineralization [5].

Young Tonalite

Intermediate Tonalite

Diorite

Volcanic breccia

681 Y. Adriansyah et al. / IJE TRANSACTIONS A: Basics Vol. 31, No. 4, (April 2018) 679-683

3. RESULT AND DISCUSSION

3. 1. Distribution of Joint Density Joint

information is one of the important aspect that need to

be determined early in the design process, this

information may have to be based solely on borehole

core and associated geophysical testing [6]. Joint

density mapping was conducted over the Batu Hijau

Mine where the location point can be safely accessed on

the bench, ramps and geotechnical slope break. The area of interest is focused on elevation below

195 mRL to the pit bottom. The total of 236 joint

density locations were mapped and covers on the three

type of lithology namely Volcanic, Diorite and Tonalite.

For further geotechnical assessment, each joint density

mapping result were plotted and processed using

GEM4D software.

Based on the statistical approach from the histogram

distribution, the joint density (JD) at the research area

was classified into 4 groups, namely:

1. JD < 15/m2

2. 15/m2< JD < 25/m2

3. 25/m2< JD < 35/m2

4. JD > 35/m2

The joint density mapping showed that the high joint

density (JD>35/m2) is located and concentrated on the

lower north wall and east wall of pit bottom. In addition,

the high joint density can also be observed on the

middle slope of northwest wall and a localized area in

the middle slope of northeast wall. Meanwhile, the joint

density in the southwest to north wall of pit bottom is

dominantly can be categorized as medium to low.

In the upper slope of east to west wall dominantly

has a joint density value ranging from 15 to 25. On the

other hand, the upper slope of north to east wall the joint

density value is very varied ranging from 15 to 35. The

distribution of joint density can be seen on the Figure 4.

3. 2. Fault Orientation The continuous work has

been conducted to review and updated the fault model,

both for major and intermediate fault. Currently, there

are more than 40 major faults and 38 intermediate faults

have been generated. In the research area, the geological structure

classification is based on the characteristic and

orientation itself, the faults can be divided into six

groups or categories. The following Table 1 is the

detailed summary of the fault grouping at the research

area; meanwhile the map can be seen in the Figure 5.

Figure 4. Map showing distribution of joint density. The color

indicates the value of joint density

Figure 5. Map showing fault distribution on the pit slope

design. The dashed color showed the location of the fault

grouping

TABLE 1. Fault grouping at Batu Hijau Mine

Fault Group Trending Dipping Location Fault Name

Group 1 East – West Moderate to steep (45° –

70°); dipping to South North and Northeast wall Ferry, Ijen, Ronni, Kerinci, Ciremai, North, & Yuli.

Group 2 Northwest –

Southeast Steep (>70°); Dipping to

Southwest North and East wall

Bromo, Merapi, Katim, Katala and ES intermedi-ate fault series. This area was defined as “fault corridor”.

Group 3 Northwest –

Southeast Moderate to Steep (45° –

70°); Dipping to Northeast South, Southwest and

Wall Tongoloka Puna, Tambora, Kelimutu, Perigi, Arjuna

and SW intermediate fault series

Group 4 Northwest–

Southeast

Moderate (±45°)Dipping to

Southwest Southwest and West wall

Tongoloka South, Tongoloka Beru, Uka-uka, Nagin,

Kawi

Group 5 North Steep (>70); Dipping to West North wall Charly, NS_3, NS_1, NS_2

Group 6 Northeast Moderate to steep (45° –

70°); Dipping to Southeast Northwest wall Sinabung, Kelud, Katala Splays

Y. Adriansyah et al./ IJE TRANSACTIONS A: Basics Vol. 31, No. 4, (April 2018) 679-683 682

3. 3. Geotechnical Domain Most of multiple

bench scale failures at Batu Hijau were structurally

controlled by major and intermediate faults, joint sets

and rock fabric. Since the joint density is one of the

structural geology characteristics/properties, therefore

assessing joint density is an important stage on

geotechnical study of the pit slope design. As a result,

the joint density distribution can be used as basic

information for constructing a structural geotechnical

domain. Human and Jupp [7] mentioned that the

joint/fracture frequency is one of the main input for 3D

wireframes modeling and define geotechnical domain. The structural geotechnical domain were interpreted

and modelled based on joint density distribution

combined and supported by structural model that

consider potential of failure type. The summary

description of each structural geotechnical domain can

be seen in the Table 2 and presented in Figure 6.

TABLE 2. Characteristic of structural geotechnical domain

Geotech

Domain Joint density group(/m2)

Fault

Grouping

Potential

Failure Type

1 15>JD> 25 Group 2 Wedge Failure

2 25>JD> 35 and JD>35 Group 2

and 6 Wedge Failure

3 25>JD> 35 and 15>JD>

25 Group 1

and 5 Planar Failure

4 15>JD> 25 Group 1

and 5

Wedge and

Planar Failure

5 15>JD> 25 Group 2 Wedge Failure

6 15>JD> 25 Group 2

and 3 Wedge Failure

7 15>JD> 25 and 5>JD>

15 Group 4 Planar Failure

Figure 6. Structural geotechnical domain based on joint

density mapping supported by structural model

4. CONCLUSION

Batu Hijau mine is porphyry copper – gold mine with

very complex of geological structure. In term of slope

stability, the geological structure will play as a major

control thus the structural model have to be robust to

address and anticipated the pit wall issue. The joint

density is one of the physical properties; also it can

reflect exposed rock mass quality. Therefore, the joint

density mapping can be used to generate the structural

geotechnical domain.

This approach for developing structural geotechnical

domain is very important and very useful since the

process is simple and low cost compared to the benefit

gained. However, this joint density information is only

based on surficial data from the exposed pit wall.

Therefore, additional information is needed to increase

the reliability of the model. In this study, the structure

model is involved to support and increase the reliability

of the structural domain, since the structural domain is

developed by surface and sub-surface data. Hence, the

structure model will provide additional information

related to potential failure type on each domain.

Furthermore, the structural geotechnical domain that

generated based on the geological information in the

particular joint density can be used as a basic for

generating detail of geotechnical domain model for

further geotechnical analysis.

The joint density mapping is effective to be

performed for generating various geotechnical purposes.

However, it should consider to safety standard and

requirement, in particular when the mapping is

conducted along the active mining and/or high risk area.

5. ACKNOWLEDGEMENT

The authors would like to thanks to Management PT

Amman Mineral Nusa Tenggara for allowing and

supporting in data collection for completion of this

paper. Furthermore, special thanks and grateful to Mr.

Hemiel Dayan Lelono for valuable discussion, and Mr.

Supardi and Mr. Dedi Maryadi who support and help

the author while performing geotechnical mapping to

obtain the joint data in the field.

6. REFERENCES 1. Garwin, S., "The geologic setting of intrusion-related

hydrothermal systems near the batu hijau porphyry

copper-gold deposit, sumbawa, indonesia", Society of

Economic Geologists Special Publication, Vol. 9, No.,

(2002), 333-366.

2. Dearman, W., "Engineering geological mapping,

Elsevier, (2013).

683 Y. Adriansyah et al. / IJE TRANSACTIONS A: Basics Vol. 31, No. 4, (April 2018) 679-683

3. Read, J. and Beale, G., "Guidelines for evaluating water

in pit slope stability, Csiro Publishing, (2013).

4. Abzalov, M., "Applied mining geology, Springer, Vol.

12, (2016).

5. Clode, C., "Relationships of intrusion, wall-rock

alteration and mineralisation in the batu hijau copper-

gold porphyry deposit", in Proceedings Pacrim Congress,

10-13 October 1999, Bali, Indonesia, Australasian

Institute of Mining and Metallurgy. Vol., No. Issue,

(1999), 485-498.

6. Galvin, J., "Ground engineering-principles and practices

for underground coal mining, Springer, (2016).

7. Human, L. and Jupp, B., "Geotechnical data collection

and presentation-it starts and ends with a vision",

AusIMM Bulletin, Vol., No. Aug 2016, (2016), 76-78.

Determining of Geotechnical Domain Based on Joint Density and Fault

Orientation at Batu Hijau Mine,West Sumbawa-Indonesia

TECHNICAL

NOTE

Y. Adriansyah, Z. Zakaria, D. Muslim, F. Hirnawan

Faculty of Geological Engineering, Padjadjaran University Bandung, Indonesia

P A P E R I N F O

Paper history: Received 14 October 2017 Received in revised form 02 January 2018 Accepted 04 January 2018

Keywords: Batu Hijau Mine Geotechnical Domain Geotechnical Mapping

چكيده

ترل عمرانی کن ق بخشقیق ناحیه معدن باتو هیجو از معادن جنوب غربی استان تنگارا اندونزی است. منطقه تحقیمنطقه تح

اختار زمین سحضور رژیم معماری فعال که غنی از ذخائر معدنی و .شده طبق طرح معماری بخش جنوبی این جزیره است

مل و ر تکاشناسی در این ناحیه است. تمرکز مطالعات بر چگونگی تکامل دامنه زمین شناسی که از اهمیت خاصی د

نهی دامطراحی معدن رو باز برخوردار است. این تحقیق نشان داده است که اطالعات زمین شناسی برای شناسای

رامترهای و پا ژئوتکنیکی زمین بسیار مفید می باشد. اطالعات حاصل از این تحقیق راهنمای مناسبی برای طراحی شیب

طر و ونه خموثر معدن روباز است که از ویژگی آن شناسائی خصوصیات ژئوتکنیکی معدن همانند تعیین و بررسی هرگ

.ریسک سقوط و خطا احتمالی ریزش معدن را بررسی نماید

doi: 10.5829/ije.2018.31.04a.21